Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$143.65	3.391%	$148.5212	$148.52	$148.50	$148.50
Purchase #2	$235.83	10.387%	$260.3257	$260.33	$260.35	$260.30
Purchase #3	$40.56	5.147%	$42.6476	$42.65	$42.65	$42.60
Purchase #4	$108.55	12.333%	$121.9375	$121.94	$121.95	$121.90
Purchase #5	$104.86	10.229%	$115.5861	$115.59	$115.60	$115.60
Purchase #6	$242.32	13.417%	$274.8321	$274.83	$274.85	$274.80
Purchase #7	$120.27	6.346%	$127.9023	$127.90	$127.90	$127.90
7 purchase totals =	$996.04		$1,091.7525	$1,091.76	$1,091.80	$1,091.60